What was found
(CAN) A CONTINUOUS SMELL OF OIL OCCURRED AFTER SETTING CLIMB POWER UPON TAKEOFF & CONTINUED FOR APPROX 2 - 3 MINUTES. SMELL WAS CONFIRMED BY ALL 4 CREW MEMBERS. CREW PUT ON OXYGEN MASKS & THE RAM VENTILATION, BLEEDS OFF. CHECKLIST WAS RUN. SHORTLY THEREAFTER THE OIL SMELL WAS CONFIRMED TO HAVE CEASED. OXYGEN USE WAS CEASED & THE ACFT RETURNED FOR AN UNEVENTFUL LANDING. CREW REPORTED SORE EYES & THROATS, REDUCED DECISION MAKING CAPABILITIES AFTER THE EVENT. TROUBLESHOOTING IN PROGRESS TO DETERMINE CAUSE OF CABIN ODOR & ISOLATE THE SOURCE. MFG WILL INVESTIGATE TO ESTABLISH ROOT CAUSE & PROVIDE INFORMATION THROUGH SUBSEQUENT SERVICE DIFFICULTY REVIEW MEETING & SUPPORTING DOCUMENTS OR OTHER AGREED UPON COMMUNICATIONS.